Nagasaki and Hiroshima are two cities in Japan that had very sad things happen to them a long time ago. In August of 1945, near the end of World War II, the United States of America dropped really big bombs on these two cities. These bombs were called atomic bombs, and they were really, really powerful.
The atomic bombs made a huge explosion that damaged everything in sight. It killed many people and hurt many others. The explosion was so big that it started fires that burned buildings and trees. The heat was so intense that it even melted things like metal and glass.
These bombs were dropped by the United States because they wanted to end the war with Japan as quickly as possible. The government thought that by using these atomic bombs, they could force Japan to surrender and end the war without more people getting hurt on either side.
Unfortunately, these bombs caused a lot of horrible things to happen. Thousands of people died in the explosions or soon afterwards from their injuries. Those who survived the immediate aftermath had to deal with radiation sickness, which is a serious condition caused by exposure to a lot of radiation. It made many people very sick and caused a lot of long-term health problems.
Today, the cities of Nagasaki and Hiroshima are important places of remembrance for people all over the world. They remind us of how powerful and dangerous these weapons are, and why it's important to find better ways to solve problems without hurting each other.